Exposure control system for flash photography

ABSTRACT

A flash exposure control system comprising a flash lighting unit, a battery circuit connected to said flash lighting unit to energize said flash lighting unit during an exposure, a switching arrangement connected to said flash lighting unit to control the termination of energization of said flash lighting unit, a timer for controlling the conduction of said switching arrangement, the timer having an adjustable circuit for adjusting the duration of conducting time as a function of the camera-to-object distance and the adjustable circuit being responsive to the camera focus adjustment, and an aperture adjusting unit responsive to the focus adjustment for defining an exposure aperture.

This is a continuation of Application Ser. No. 375,033 filed June 29,2973, and now abandoned.

This invention relates to a flash exposure control system, and moreparticularly it relates to a flash exposure control system capable ofproviding accurate flash exposure values over a wide range of flashlighting situations ranging from an object at a relatively longerdistance to an object at a superclose distance.

In order that the quality of photographs taken with an auxiliary lightsource such as flash photographic equipment is acceptable, it is wellknown that by determining the camera-to-object distance L and lightenergy available from the employed flash unit or the so-called flashguide number G_(NO), photographers generally make use of formula F =G_(NO) /L to compute the camera lens aperture opening F, and then evolvea flash exposure value in conformance therewith. In some cameras andflash units hitherto proposed, the formula is automatically computed bya computing mechanism incorporated in the camera or the flash unitassociated with the camera, thereby the area of the camera lens apertureopening is automatically adjusted in response to the focus adjustment ofthe camera.

Such conventional computing mechanisms adapted for use in flashphotography are limited in the ability of automatically evolving flashexposure values as a function of the camera-to-object distance, owingboth to the limitations of the camera lens aperture adjustment range andto the limitation of light energy level of the flash unit, so that anarrow object distance range limited thereby makes it difficult to yieldthe correct exposure for photographic situations which may beencountered at infinite to exceedingly close positions.

In order to make up for such a deficiency, a proposal has been made.According to the proposal, the reflected light from an objectilluminated with flash light of the energized flash unit is integrated,and when the integrated intensity of light reaches a predeterminedvalue, the energization of the flash unit is terminated to effect thecorrect exposure. Such a flash exposure control device is known as theso-called "Computer stroboscope". However, although the proposal hassucceeded in the removal of the limitation with regard to theillumination energy, the problem attendant on the limitation of theaperture adjustment range remains unsolved, because the device isdesigned to control the light energy of the flash unit in conformancewith the selected diaphragm value. Thus, similar to the former, it isyet difficult to evolve flash exposure values as a function of thecamera-to-object distance over a very wide range.

Particularly when an object to be photographed is situated at a so closedistance that an aperture opening smaller than the minimum openingavailable in the diaphragm control device of the camera is necessary, itis impossible to make the correct exposure. Therefore, in this case, itis usual to modify the alignment of the stroboscopic unit used forilluminating the object with view field of the camera so as to decreasethe effective illumination energy level.

So long as such conventional techniques are utilized, however, thephotographer must modify a derived exposure value based on his personalexperience of high standard, or make a series of bracketed exposure atdifferent exposure values by trial-and-error approach to assure theselection of at least one appropriate exposure value.

Further, in case the stroboscope is used as a flash light source inclose range flash mode, as the interval between the optical axis of thecamera lens and the stroboscope is decreased being appreciable withrespect to the camera-to-object distance, the flash light distributioncharacteristic of the stroboscope has a stronger effect on theuniformity of illumination for the object. In order to alleviate thisdisadvantage, O-shaped stroboscopic Xenon tube is employed to be mountedon the front end of the lens barrel. However, the employment of such atype stroboscopic unit is not intended to solve the problems attendanton the derivation of accurate flash exposure values, and, in an extremecase, causes an object being photographed to be illuminated in a ringshape, so that the luminance of the center of the object is decreased ascompared with other parts.

The present invention has overcome the above-mentioned conventionaldrawbacks and disadvantages, and, therefore, it is an object of theinvention to provide a flash exposure control system capable ofproviding accurate flash exposure values over a wide variety ofphotographic flash light situations including from an object at arelatively longer distance to an object at an extremely close distance.

Another object of the invention is to provide a photographic flash lightdevice adapted for use with the flash exposure control system, whichpermits the camera coupled therewith to make correct exposure whenoperating in close and superclose range flash mode.

It is also an object of this invention that the flash exposure controlsystem may take the form of a complex system having extended rangecapability such that accurate flash exposure values for an object at ausually encountered distance are derived by controlling the guide numberor the light energy of a flash equipment with the automatic adjustmentof camera lens aperture, while an object at an extremely close distanceis illuminated with flash light of an illumination energy levelcontrolled by modifying the alignment of the flash unit, thereby acorrect exposure is effected without the necessity of controlling theguide number.

Other objects and advantages of the present invention will be obvious tothose skilled in the art from the disclosure hereinbelow.

In the drawings, wherein like reference characters indicate like orcorresponding parts;

FIG. 1 is a schematic representation of a conventional flash autosystem.

FIG. 2 is a schematic representation of a flash exposure control systemaccording to the present invention.

FIG. 3 is a schematic electrical control circuit for governing theoperation of the system of the invention.

FIG. 4 is a schematic view of the automatic diaphragm control device ofthe invention.

FIG. 5 is a chart depicting a correlation of guide number with lensaperture and object distance.

FIG. 6 is a horizontal sectional view illustrating diagramatically theoperation of the invention when an object at a superclose distance isphotographed in flash mode.

FIG. 7 is a chart having the same indicia as used in FIG. 5, and showinga series of characteristic curves for defining the operation of theflash exposure control system according to the invention.

FIG. 8 is a horizontal sectional view illustrating diagramatically theoperational feature of the present system shown in FIG. 6 with amodification when an object at a superclose distance is photographed inflash mode.

FIG. 9 is a perspective view of a photographic flash light deviceadapted for use with an photographic device incorporating the system ofthe present invention capable of superclose photography.

FIG. 10 is a front elevational view of the flash device shown in FIG. 9.

FIG. 11 is a side view of the device shown in FIG. 9 in attachment witha camera lens barrel.

FIG. 12 is a front elevational view of the device shown in FIG. 9,partially in section.

FIG. 13 is a top plain view of the device shown in FIG. 9, partially insection.

FIG. 14 is a vertical section taken along the line B-B' in FIG. 10.

FIG. 15 is a circuit diagram including the circuits of the device shownin FIG. 9 and the exposure mechanism of the camera.

The theoretical background on which the present invention is explainedhereinbelow. It is assumed that as shown in FIG. 6, an illuminationlight source such as a stroboscopic unit S having a discharge tube 1 andparabolic reflector 2 is arranged to shoot toward the center 3 of anobject O to be photographed. The light unit is aligned along an angle θwith respect to the photographic axis of an objective lens 5 having andiaphragm D of a camera C rising a photographic film f. The center 4 ofthe film and the center of the lens are aligned with the center 3 of theobject O. The time variable luminance E(o) at the center 3 of the objectO in the direction to the objective lens 5 defined by

    E(o) = [RP/L.sup.2 ]cos θ                            (1)

wherein P is the flash output of light source 1 in terms of Beam CandlePower Second; R is the reflector characteristic of the reflector 2; andL is the distance from the light source 1 to the object center 3. Thetime variable luminance B(o) at object center 3 in the direction to thecamera lens 5 defined by

    B(o) = E(o) r/t                                            (2)

(wherein R is the diffuse reflectance of the object O). The luminanceI(o) at the film center 4 is defined by ##EQU1## (wherein F is theaperture value of the camera lens 5; N is the sensitivity of the film f;t is the transmittance of the camera lens 5; and M is the magnificationof image)

In general, the formula necessary for evaluation of exposure values isgiven by the following equation:

    B · T = K · F.sup.2 /N                   (4)

(wherein R is an exposure time; and K is a constant) In mostphotographic situations, the left side of equation (4) may be consideredto be essentially equal to the time variable luminance of the objectexposed to the flash light when photographing in the flash mode. Hence,exposure values for such photographic situations may be evaluated basedon the following equation (5) derived from equations (1) - (3): ##EQU2##In equation (5), the film sensitivity N, constant K, reflectorcharacteristic r are those previously given. However, one of thevariables F, L, R, P and θ should be modified in accordance with imagemagnification M to derive accurate exposure values.

Equation (5) is particularly relevant to the evaluation of exposurevalues for an object at a relatively close distance-variations. However,of R, θ and M may be considered to be negligible, when equation (5) isused to evaluate flash exposure values for an object at a usuallyencountered distance.

Hence, for the usual focusing distances, equation (5) is reduced to thefollowing equation.

    F · L = a √ NP                             (6)

(wherein a is constant) The right side of the equation (6) is usuallycalled "guide number", which is often used to compute the camera lensaperture F when photographs are taken using an auxiliary illuminationlight source.

This relationship is graphically illustrated in FIG. 7. When astroboscopic unit having a guide number of 16 is used with a camerahaving a diaphragm control device capable of aperture adjustment betweenF2 and F22, it is apparent from equation (6) that the curve B₁represents the camera lens aperture opening which may be required at theselected object distance. In other words, it is possible to set thecorrect exposure for flash lighting situations so long as an objectbeing photographed is posed within a range of distances from a nearpoint of 0.75 meter to a far point of 8 meters. However, when an objectat a distance of less than 0.75 meter is photographed, the light energyrepresented by the guide number 16 is too large to effect the correctexposure.

It is evident from the equation (6) that if the flash energy P isdecreased, it is possible to obtain the correct exposure for an objectat a distance of less than 0.75 meter. For example, when the guidenumber is decreased to 5 to 6, the correct exposure is effected for anobject at a distance of as short as 0.250 meter as can be seen from thecharacteristic curve B₂ in FIG. 7. Thus the decrease in the guide numberof the stroboscopic unit extends the object distance range toward to theshorter positions range, the resulting range being as wide as 0.250 to 8meters as shown by characteristic curve A in FIG. 7.

However, such a further decrease in the flash energy of the stroboscopicunit which extends the range toward this shorter distance is not valid,because equation (6) was based on the assumption that an object to bephotographed is situated in a usual distance L.

In photographing an object at a superclose distance, the imagemagnification M has a large effect on the evaluation accuracy ofexposure values. This as mentioned before, at least one of the variablesF, L, R, P and θ should be corrected on the basis of the value M.Further, a decrease in the light energy of the flash device causes theflash light distribution characteristic of the discharged tube tochange. Thus a very difficult problem would be created in the process ofachieving a theoretical compensation for the variation of M.

An object of the invention is to impart a continuous or stepwiseadjustment of the flash light shooting angle into an exposure controlsystem when performing the superclose flash photography, thereby toyield a correct exposure with high accuracy, while still maintainingconstant the flash output level.

The feature of the invention will be explained on the basis of thetheoretical equations. When the flash shooting direction deviates by anangle θ from the alignment with the field of view of the camera, theeffective flash output Pe defined by Pe = RPcos θ is varied withvariation of the angle θ. Therefore, equation (5) may be rewritten as##EQU3##It is apparent from equation (7) that to obtain a correctexposure for an object at a superclose distance, one should in practicecontrol the effective flash energy Pe in accordance with distance L andmagnification M. This is so, because the valve F cannot be decreasedfrom the minimum aperture value of the camera. So long as the flashenergy P is constant, Pe depends on only the flash light distributioncharacteristics which can be determined experimentally. Thus unstablefactors which would arise if the flash energy level is varied areremoved. In this case, the angle θ may be varied either in such mannerthat when the object distance is decreased from a usual one tosuperclose one, the angle is discontinuously changed to such a valuethat the correct exposure is effected only when the object is situatedat the superclose distance, for example, at a distance of 0.125 meter,or in such manner that the angle is continuously varied in accordancewith the object distance so as to make the correct exposure over theentire range of, for example, from 0.125 meter to 0.250 meter.

In connection with the latter, FIG. 8 depicts the operation of the flashexposure control system. Here the distance-adjusting ring of a cameralens barrel 5 is provided with a cam arrangement 5₁. Two cam followers5₂ and 5₃ slidably engage the cam arrangement 5, to vary the flash lightshooting angle θ of flash units 2 and 2' with respect to the opticalaxis. As mentioned above, when the flash angle is varied, the flashenergy may be kept constant. Thus the right side of equation (7) dependson only the magnification M and constant a. For example, suppose thatthe calculated value of the right side is four, and the flash angle isdiscontinuously changed to a value at which the discharge tube isdirected toward the center of the object at a distance of 0.125 meter.Then, the correct flash exposure is effected only for the supercloseobject as shown at point M₁ in FIG. 7. On the other hand, when the angleis continuously varied with the object distance, the correct exposure iseffected for any object so long as it is posed in a range of 0.125 to0.250 meter as shown by M₂ curve in FIG. 7.

As can be understood from FIG. 7, responsive to both the usual distanceand a relatively closer or superclose distance, the system of theinvention is capable of providing exposure values for continuousvariation of the flash lighting situations as shown by a programcharacteristic A, B, or B₂.

Preferred embodiments of the invention are explained with reference tothe accompanying drawings. FIGS. 2 - 5 illustrate one embodiment of theflash exposure control system capable of evaluating flash lightingsituations at usually encountered distances according to the presentinvention. The outline of the constructional feature of the system ofthe invention is described herebelow. In prior art systems, apertureadjustment is effected by computing the guide number and determining thecamera-to-object distance as shown in FIG. 1. According to theinvention, the aperture opening and guide number are simultaneouslyadjusted to a set of values in comformance with the selectedcamera-to-object distance. FIG. 5 is a chart correlating the flash guidenumber with the distance and diaphragm value. In a case where a flashphotography is performed using a flash unit having a guide number of 22and a camera with a F2 lens, inasmuch as the camera lens apertureopening is adjustable in a range of F2-F22, the correct exposure will bemade for an object at a distance ranging from one meter to elevenmeters, but not for an object at a distance, for example, of 0.5 meter.In order to make the system responsive to the latter distance, thepresent invention contemplates to vary the guide number in accordancewith the distance either in a continuous manner as shown by broken linesC, or in a stepwise manner as shown by chain lines A and B. FIG. 4illustrates an automatic diaphragm control device associated with ameter 15 constituting an exposure meter circuit including a battery E₂and a photosensor P. An arm 20 a of the diaphragm ring 20 engages with apin 11 of a pointer-scanning member 7 having cam teeth surfaces 9 and isnormally attracted by spring 19 to keep the diaphragm blades not shownin an unblocking position. The reference numeral 1 is a release leverslidably mounted in engagement with guide pins 2a and 2b, and attractedupward by means of a strong spring 4. Numeral 6 is an intervening leverpivotally mounted at a bearing, one arm of which engages the releaselever 1 at pin 3, and the other engages the scanning member 7 at pin 10,so that the scanning member 7 is urged by the force of spring 4 againstspring 26 to disengagement from the meter needle 15'.

Numeral 21 is a change-over ring for changing over EE photography andflash auto photography to each other which is arranged to operateswitches S_(A) and S_(F) of the exposure meter circuit by means of a pin21a mounted on the arm thereof. Numeral 23 is a distance-adjusting ringhaving brushes mounted on the arm thereof to slide on variable resistorsVR₁ and VR₂.

Numeral 18 is a film sensitivity calibrated disk rotatably mounted at ashaft 16, and a gear 17 fixed on the disk 18 engages a gear 14 fixed onthe meter casing so that a rotation of a calibrated disk 18 causes themeter casing to rotate about the shaft 13, thereby the position of meterneedle is varied in accordance with the film sensitivity.

When the mark A on the change-over ring is aligned with the symbol mark22, switch S_(A) is closed and S_(F) is open so that the meter needle ismade responsive to the intensity of light received by photosensor P topermit the usual EE photography, while when mark F is aligned withsymbol mark 22, switch S_(A) is open and switch S_(F) is closed, so thatthe variable resistor VR₁ is connected to meter 15 and battery E₂. Arotation of distance-adjusting ring 23 for the focus adjustment variesthe resistance value of the variable resistor VR₂ in accordance with thedistance so that the meter needle 15' is deflected to a position inconformance with the selected distance. When release lever 1 is pusheddown, the scanning member 7 scans the position of the deflected needleto determine the amount of rotation of the diaphragm ring, as a resultof which the area of the aperture opening is automatically adjusted inthe same way as in the EE photography.

Simultaneously responsive to the rotation of the distance-adjusting ring23, the resistance value of the variable resistor VR₂ is varied so thatthe time constant circuit comprising C₂ and VR₂ shown in FIG. 3 iscapable of controlling the guide number in accordance with the distance.

Referring to FIG. 3, a battery E₁ for stroboscope is used to charge themain capacitor C₁ at a voltage boosted by an oscillation boostercircuit. When the shutter is released, the synchronous contact X isclosed to transmit a pulse through a trigger circuit to the triggerportion of the stroboscopic discharge tube T and to the gate of SCR₁,thereby SCR₁ is driven to "on" state, and T is energized. C₄ designatesan auxiliary capacitor. When a current flows through T, a currentgenerated in the secondary coil of a pick-up transformer PU actuates thetime constant circuit C₂, VR₂ through a rectifier circuit. After apredetermined time has passed, SCR₂ is driven to "on", so that SCR₁ isreverse biased between the anode and cathode to its not-conductingstate, thereby the energization of discharge tube T is terminated. C₃designates a commutation capacitor.

As will be seen from the foregoing description, by uniquelyinterrelating the automatic aperture adjustment in accordance as afunction of camera-to-object distance and the adjustment of the flashlight energy level which is effected also in accordance with thecamera-to-object distance, the invention provides an easily manageableflash auto device which is responsive to a wide range of flash lightingsituations which may be encountered.

FIG. 6 - FIG. 15 illustrate another embodiment of the present inventionmodified so as to provide a flash exposure control system capable ofderiving accurate exposure values for an object at a superclosedistance.

Referring to FIGS. 9 - 11, reference numerals 101 and 102 indicatestroboscopic units having light-permeable filter plates 103 and 104mounted in their respective flash windows. The stroboscopic units whichare pivotable about bearings 105₁, 105₂, 106₁ and 106₂ are carried onfork-like arms 108, 109, 110 and 111 projecting from a cap 107 that isattachable to a camera lens barrel. The cap 107 is further provided withillumination light source housings 112 and 113 having condenser lenses112, and 113, mounted on upper and lower portions of the front surfaceof cap 107 respectively. These are used to illuminate the center of anobject when operating the focus adjustment for an object at a superclosedistance so that the distance adjustment operation of the photographiclens is easily carried out. A selector switch or change-over means 114provides three selection positions according to the focal lengths of thecamera lens f═50mm and f═100mm and manual operation M. A lock-releasingmember 115 is used for detaching the cap 107 from the lens barrel.Switching or change-over pins 116 and 117 switch over microswitches tobe described hereafter and are arranged to be pressed by portions of thestroboscopic units when the stroboscopic units are pivoted to positionsindicated by broken lines in FIG. 9 to change the flash angle. FIG. 11illustrates an attachment of the cap 107 carrying the stroboscopic unitsshown in FIG. 9 and FIG. 10 to the lens barrel of camera C.

Referring to FIG. 12, the stroboscopic unit 101 or 102 is pivotallysupported between bearings 105₁ and 105₂, or 106₁ and 106₂ respectively.The pivotable movement is controlled by means of rebound clip arm 118 or119 mounted on shaft 105₁ or 106₂ to secure the stroboscopic unit at theposition indicated by the broken lines shown in FIG. 9. In FIG. 12, thestroboscopic units 101 and 102 are illustrated as having xenon tubes 121and 123 fixed at the center of the reflectors 120 and 122 respectively.

Referring to FIG. 13, a plastic ring 107₁ having a rectangular channelbroached therein is rigidly mounted inside the cap 107. A board coverplate 107₂ is fixed on the ring 107₁ to make a space with the channel inwhich a ring resistor 107₃ is mounted. Coaxially and movably secured inthe ring 107₁ is a sleeve 107₄ which is connected to sliders 107₇ and107₈ through connection rods 107₅ and 107₆, so that a rotation of sleeve107₄ permits the sliders 107₇ and 107₈ to slide on the resistor 107₃,thereby to provide two rheostats. Rigidly mounted on sleeve 107₄ is anengaging member 107₉ having a channel-like key receiver in such anarrangement that when the cap 107 is attached to the lens barrel asshown in FIG. 14, a pin l₁ mounted on the distance-adjusting ring of thelens barrel is urged to engagement with the key receiver by insertionthereto.

Referring to FIG. 14, the cap 107 is provided with a bayonet receiver124 mounted rigidly therein which when engaged with a bayonet l₂ securedon the front end portion of lens barrel L permits the cap to be securedon the front end of lens barrel L, while the engaging member 107₉ isengaged with the distance adjusting ring pin l₁ on the lens barrel.

In order to make the above-mentioned construction ready for flashphotography, an operator attaches the cap on the front end portion ofthe lens barrel of a camera C, while engaging respectively the keyreceiver of engaging member 107₉ and bayonet receiver 124 with the pinl₁ and bayonet l₂, and rigidly secures the cap 107 on the front end ofthe camera lens barrel L as shown in FIG. 11. Here numeral 125 indicatesan electric circuit control unit for the stroboscopic units 101 end 102,and character H indicates a flash coupler.

Referring to FIG. 15, a connection diagram is illustrated as includingthe electric circuits incorporated in the stroboscopic units 101 and102, the ring channel of cap 107 and the control unit 125. The circuitof control unit 125 comprises a direct-current voltage booster circuitC₁, a constant voltage G₂ and a flash output control circuit G₃. Thebooster circuit G₁ which is of the known type is so constructed that theoutput of the booster transformer OSCT after rectified by diode D isdirected to the main capacitor C1 of which the terminal voltage isdivided by a bleeder resistor R₅ and R₄, and is detected by a Neon tubeN₁ to control the termination of the oscillation through a controltransistor Tr₃. At the same time, the voltage across the main capacitorC1 is divided by another bleeder resistance R7, R6 and detected byanother Neon tube N2, so that when the voltage of the main condenser hasreached a predetermined value, the Neon tube N2 is allowed to discharge,and this causes transistor Tr7 to conduct with the result that aconstant voltage output is formed which is applied through a flashcoupler H to the exposure control circuit of the camera. The controlcircuit G₃ comprises a flash current detecting transformer T2, a diodeD4, a capacitor C2, a program conjunction transistor D5, a condenser C3for time constant, a trigger SCR₁, a trigger transformer T₃, a quenchingtube Q₁, triggers SCR₂ and SCR₃. The two Xenon tubes 121 and 123 ofstroboscopic units 101 and 102 are connected to each other in series,and connected through SCR₂ to the main capacitor C₁ for energization ofthe flash units. The connection of the Xenon tubes, and moreover theduration of flash light time is extended, as disclosed in our copendingJapanese Pat. applications Nos. 47-24497 and 47-24498.

The two rheostats VR₁ and VR₂ comprising the resistor and sliders in cap107 are changed over by means of the changeover means 114 interlockingwith switches SW₈ and SW₉. The rheostat VR₁ is connected to thediaphragm indicator M incorporated in the exposure meter circuit of thecamera C, while the other rheostat VR₂ is connected to condenser C₂ ofcontrol circuit G₃. Switch SW₆ and SW₇ in cap 107 are changed over bymeans of change-over pins 116 and 117. The switches are set to contactsNC when an object at a usual distance is photographed. They are switchedto contacts NO by means of pins 116, 117 which are pressed upon thepivoting of the stroboscopic units 101 and 102, to the positionsindicated by the broken lines, when an object at a superclose distanceis photographed. In the former case, at usual distances the diaphragmvalue indicated in the indicator as well as the light energy availablefrom the Xenon tubes of the stroboscopic units is varied in accordancewith the object distance. On the other hand, in the latter case atsuperclose distances, both the exposure meter circuit and flash energycontrol circuit for the Xenon tubes are made irresponsive to the focusadjustment. The output of the secondary coil of detection transformer T₂is applied through a diode D₄ to a smoothing condenser C₂. Applied onthe timing condenser C₃ is a direct current voltage of almost constantlevel through the resistor R₉ and the resistor VR₂ or r₁. Theconjunction transistor D₅ permits the condenser C₂ to be instantaneouslycharged at the starting point of flash current. After an interval oftime dependent on the time constant based on the resistance of VR₁ or r₁and the capacity of capacitor C₃, the completion of charging capacitorC₃ causes it to conduct, as a result of which the voltage generated inresistor R₁₃ makes SCR₁ conductive to leak away the charge on condenserC₄ through transformer T₃, trigger the quenching tube Q₁ and leak awaythe residual charge on the main capacitor, terminating the energizationof the Xenon tube 121 and 123.

Therefore, the duration of energization of the Xenon tubes is controlledin accordance with the object distance, when they are connected to VR₂,while when the object at an extremely close distance is photographed,the duration of energization dependent on the value of resistance r₁, iskept constant. The transistors Tr₃ and Tr₄ are switching transistors andare made conductive by the discharge of Neon tube N₂. When transistorTr₅ is "on", a constant current flows between the gate and drain oftransistor Tr₆ and applied to the base of transistor Tr₇. As a result,the transistor Tr₇ is made conductive and a forward current flowsthrough diode D₃ to form a constant voltage output at the anode terminalof the diode. The constant voltage output is forwardly directed to thebattery E1 of the flash coupler H.

As a result, the meter M of the exposure meter circuit and E1-M-VR1, orr2-D3-E₁ form a closed circuit. Moreover, the meter M is responsive tothe resistance of resistor VR1 or r1, because the diode D₃ is biasedforward. On the other hand, the voltage generated across the diode D₃ isapplied through a synchronous switch Sx to the gate of SCR₆ as a triggervoltage, and to the trigger transformer as a trigger current. The switchSW₃ is used to change the number of discharges. When it is connected toeither R or L, one of the Xenon tubes 101 and 102 is energized, whilewhen connected to BOTL, the both Xenon tubes are simultaneouslyenergized. L1 and L2 designate illumination lamps incorporated in theillumination housings 112 and 113. When resistor r1, or r2 is selected,the quantity of light energy of the Xenon tube is decreased to four interms of guide number.

Next, the operation of the circuits shown in FIG. 15 will be explainedhereinbelow. When the control unit 125 is connected to a camera Cthrough the flash coupler H, a wiring among the circuits of the controlunit 125, the flash coupler H and the camera C is established, and thecontrol unit 125 is connected to stroboscopic units through a cable, sothat the total circuits are made operative thereby.

When the main switch Sw is closed, the booster oscillation voltagecircuit G1 is connected to the battery E2, and the boosted voltage isapplied to the main capacitor C1. When the voltage of the capacitor C1reaches a predetermined voltage level, a voltage generated in theconstant voltage circuit is applied to the meter circuit of the camera Cthrough H, so that the meter is made operative. In this state, when anobject being photographed is situated at a usual distance, switches SW₆and SW₇ are connected to contact NC, so that VR₁, VR₂ are adjusted inconformation with the selected object distance. The selected VR₁ valuedetermines the flash output P according to program A shown in FIG. 7.Next, when the release mechanism of a camera not shown is actuated, thesynchronous contact is closed, so that the energization of the Xenontubes is started by the flash output control circuit G3, and the flashoutput P is controlled by the flash output control circuit G2 inconformation with the selected VR₂ value.

When the stroboscopic unit is aligned with an object at a superclosedistance, switches SW₆ and SW₇ are automatically changed over from NC toNO contacts so that the VR₁ and VR₂ are replaced by fixed resistors r1and r2, thereby the diaphragm value F and flash output P is maintainedconstant. In order to effect uniform illumination for the object, theflash light portions S2 and S3 shown in FIGS. 7, 9 and 10 are inclinedat an angle θ with respect to the optical axis.

When switches SW is closed, the illumination lamps L1 and L2 illuminatethe object so that the focus adjustment is easily carried out.

The flash lighting portions S2 and S3 of the stroboscopic units 101 and102 are arranged in parallel with the photographic axis, when an objectat usual or relatively close distance is photographed.

When the object distance falls in the superclose distance range whichmay be indicated by means of a meter of a camera, the flash lightingportions S2 and S3 are inclined through an angle θ to the photographicaxis so that the switches SW₆ and SW₇ are changed over to replace VR₁and VR₂ with r1 and r2, thereby the diaphragm value T and the flashlight energy P are irresponsive to the focus adjustment, thus remainingconstant.

The values of flash angle and flash output may be varied with thevariation in the object distance, or in the alternative they may befixed at such values that exposure errors are minimized. The embodimentsof the invention employs the latter case, but experimental results showthat exposure errors are negligible.

Further the embodiments are illustrated as including two stroboscopicunits, but the embodiment may be modified as including only onestroboscopic unit. Even in this case, a similar evaluation of flashexposure values may be made.

As will be seen from the foregoing description, the present inventionprovides the exposure control system capable of deriving both exposurevalues for photographic situations which may be encountered at usualdistances and flash exposure values for flash lighting situations at asuperclose distance range with very high accuracy and in foolproof,thereby to provide additional advantages to wide applications of flashlighting equipments such as stroboscopic units to flash photography,because the number of flash lighting photographic situations isincreased along the extended range of the object distance. In theaforementioned embodiments, the devices which extend the range overwhich the camera is capable of utilizing light from the flash when thecamera is focused on close objects, may be referred to as rangeextending means. The structure which simultaneously applies inputscorresponding to the position of the focusing arrangement into theaperture control and the circuit that energizes the flash, may bereferred to as entering means.

What is claimed is:
 1. A flash exposure control system for use with a photographic camera comprising:flash lighting means; circuit means connected electrically to said flash lighting means to energize said flash lighting means; angle changing means engageable with said flash lighting means to change the flash angle of said flash lighting means on the basis of distance to an object, said changing means being operative for changing the flash angle of said flash lighting means over a first set of angles corresponding to distances from the object greater than a given distance, said changing means being operative for changing the flash angle of said flash lighting means over a second set of angles corresponding to distances less than the given distance; light energy control means coupled to said flash lighting means and coupleable with said angle changing means for controlling the light energy level of the flash lighting means in a first range when the flash angle varies within the first set of angles, said light energy controlling means being operative for controlling the level of the light energy in a second range when the flash angle varies within the second set of angles, the light energy level in the first range being dependent upon the flash angle, the light energy level in the second range being less dependent on the flash angle than in the first range.
 2. The flash exposure control system of claim 1, wherein said light energy control means when coupled with said angle changing means controls the light energy level of the flash lighting means in conformance with the flash exposure value based on the formula defined by

    F · L = (1/M+1) · a · √N Pe

wherein Pe is the effective flash light energy; L is the camera-to-object distance; M is the magnification of image; F is the diaphragm value; and N is the film sensitivity.
 3. The flash exposure control system of claim 1, wherein said light energy control means is provided with a light energy control branch circuit which is made operative in response to the flash angle being within the first set of angles, said branch circuit comprising:switching means connected to said flash lighting means for controlling the termination of energization of flash lighting means; and timing means for controlling the conduction of said switching means, said timing means having adjustable circuit means for adjusting the interval of conducting time dependent on the camera focus adjustment.
 4. The flash exposure control system of claim 1, wherein the light energy control means controls the light energy level of the lighting means at near distance-range shooting in conformance with the flash exposure value based on the formula defined by

    F·L = (1/M+1) · a · √NPe

wherein Pe is the effective flash light energy; L is the camera-to-object distance; M is the magnification of image; F is the diaphragm value; and N is the film sensitivity.
 5. The flash exposure control system of claim 1, wherein the lighting means include a pair of electric flashing tubes, and the angle changing means comprise a pair of bracket means for holding pivotably each of the lighting means for adjusting the flashing angle of the flashing tube swingable toward the object.
 6. A flash device for use with a camera having an objective with a distance adjusting component as well as a diaphragm regulating mechanism having impedance means coupled with the distance adjusting component: comprising a flash unit including support means for rigidly securing the unit to the camera and illuminating means rotatably mounted on said support means, said illuminating means including angular position setting means for varying the direction of illumination with respect to the optical axis of the objective, control circuit means connected to said illuminating means and mounted on said support means, said control circuit means including a timing circuit for controlling the time of energization of said illuminating means and having an impedance means for varying the energization time, said impedance means of said timing circuit when said flash unit is secured to the camera being coupled to the distance adjusting component to vary the energization time, a flash lighting source electrically connected to said flash unit and having a power source and a control circuit connected to the output of said power source, said control circuit including a switching circuit connected between said illuminating means and said power source and a control signal forming circuit, said control signal forming circuit being connected to said impedance means of said timing circuit and to said switching circuit to apply a light control signal to said switching circuit corresponding to the selected distance.
 7. A flash device as in claim 6, wherein said flash unit includes means for linking said illuminating means to said distance adjusting component for deflecting said illuminating means.
 8. A flash device as in claim 6, wherein said support means is shaped in the form of a ring and said illuminating means are mounted on the periphery thereof.
 9. A flash device as in claim 6, wherein said support means include a right and left side and said illuminating means comprises a pair of illuminating portions mounted on the right and left side of said support means and tiltable so that the lighting directions of the illuminating means are variable independent of each other.
 10. A flask device for use with a camera having an objective with a distance adjusting component as well as a diaphragm regulating mechanism having impedance means coupled with the distance adjusting component: comprising a flash unit including support means for rigidly securing the unit to the camera and illuminating means rotatably mounted on said support, means, said illuminating means including angular position setting means for varying the direction of illumination with respect to the optical axis of the objective, control circuit means connected to said illuminating means and mounted on said support means, said control circuit means including a timing circuit for controlling the time of energization of said illuminating means and having an impedance means for varying the energization time, said impedance means of said timing circuit when said flash unit is secured to the camera being coupled to the distance adjusting component to vary the energization time, a flash lighting source electrically connected to said flash unit and having a power source and a control circuit including a switching circuit connected between said illuminating means and said power source and a control signal forming circuit, said control signal forming circuit being connected to said impedance means of said timing circuit and to said switching circuit to apply a light control signal to said switching circuit corresponding to the selected distance said control circuit comprising;adjusting means associated with the illuminating means and operatively connected to the impedance means so as to adjust the timing circuit to the shortest timing operation when the illuminating means is rotated. 